This invention relates to ionographic imaging members and, more particularly to ionographic imaging members comprising an electrically conductive layer and a dielectric layer.
In ionography, a latent image is created by writing on the surf ace of the imaging member with an ion head. The imaging member is preferably electrically insulating so that the charge applied by the ion head does not disappear prior to development. Therefore, ionographic receivers possess negligible, if any, photosensitivity. The absence of photosensitivity provides considerable advantages in ionographic applications. For example, the electroreceptor enclosure does not have to be completely impermeable to light and radiant fusing can be used without having to shield the receptor from stray radiation. Also, the level of dark decay in these ionographic receivers is characteristically low, thus providing a constant voltage profile on the receiver surface over extended time periods.
Electroreceptors are useful in ionographic imaging and printing systems such as those commercially available as the Xerox Corporation 4060(tm) and the Xerox Corporation 4075(tm), which utilize an electrically resistive dielectric image receiver, i.e., an electroreceptor. In one simple form of the systems, latent images are formed by depositing ions in a prescribed pattern onto the electroreceptor surface with a linear array of ion emitting devices or ion heads, creating a latent electrostatic image. Electrostatic images of sufficient electric field and potential are created and retained at the surface of the electroreceptor. The latent image may be formed by applying a surface charge density on the receiver surface of from about 10 to about 100 nano-Coulombs per square centimeter. These electrostatic patterns are suitable for development with toner and developer compositions.
To develop latent images, charged toner particles are passed over these latent images, and the toner particles remain where a charge has previously been deposited. This developed image is then transferred to a substrate such as paper, and permanently affixed thereto.
An alternative developing method is liquid immersion development. In a liquid development process, a charged imaging surface is passed through a liquid medium which includes toner particles dispersed in a liquid carrier. Liquid development processes typically use a low molecular weight hydrocarbon as the liquid carrier.
A typical ionographic charge receiver, schematically shown in FIGURE 1, includes a conductive substrate 11 and a dielectric layer 12 positioned over the substrate 11. The substrate 11 depicted in FIGURE 1 is in the shape of an endless seamless belt.
It is important that the dielectric layer act as a loss-less capacitor, since the purpose of the dielectric layer is to store electric charge on its surface, minimizing the amount of charge that leaks therefrom. Any such leakage makes it necessary to provide greater amounts of charge initially. Similarly, it is preferable to provide a dielectric layer which does not permit charge to migrate into the bulk of the dielectric layer, which results in instabilities in capacitance and degrades image formation.
Prior art dielectric layers sometimes become degraded during use so that their loss-less character is impaired. Similarly, degradation can increase the possibility of charge migration in the dielectric layer. Thus, it is important that the dielectric layer be resistant to its operating environment, in particular, resistant to degradation brought about by the powerful oxidants and U.V. light emitted by corona charging devices which are typically used to form charge images. The dielectric layer should also have properties which are not substantially altered by changes in the temperature or humidity of its operating environment. Since typical toning and cleaning operations can be quite abrasive, it is important that the dielectric layer also be able to withstand significant abrasion, scratching and other physical wear related contacts.